Finally, there are references. References are a key part of creating reliable information on Wikidata. Without references, it's impossible to evaluate the quality or accuracy of the information on Wikidata.
You may notice that the value has a Q number of its own. That isn't always the case; many values are simply numbers or text. But when the value is a thing (in this case, a college at Cambridge), it needs to be a Wikidata item itself.
What happens if the item doesn't exist? In that case, you'll need to create it.